in my opinion and experience.. an Indirect cylinder always superior than a combination boiler, Combi is just for space saving. Cylinder provides back up hot water and allows for solar PV input.
We used to (in the 00s) spec all our cylinder installs with Solar coils, but over the last 15-20 years we have seen solar PV pretty much make solar Thermal obsolete.
Much better to use a Immersion Relay on your solar PV (like a Eddi unit for example) to heat your water. Simpler and cheaper to maintain with increased flexibility.
We offer high recovery coil cylinders on Fossil fuel boiler installs, and mandatory on ASHP.
A correctly designed / installed / commissioned R290 ASHP on the correct tariff will be cheaper to run than any oil or gas boiler ...IN THE RIGHT PROPERTY.
A badly designed/installed ASHP will always cost more to run than a badly designed installed oil / LPG boiler system.
Install costs on ASHP can be comparable to oil by the time you factor in oil storage and there is 0% Vat on ASHP installs, which can also stretch to include the whole heating system. On a barn conversion which may be 5% or 20% vat the difference in Vat can influence decisions. (Even without the BUS Grant)
I feel that I have a fairly balanced view on all this, as we install Oil / LPG / Gas and ASHP and GSHP systems and favour none. All it depends on the property and the customer as to which is suitable.
Most dedicated ASHP installers are blinkered, up their own asses and holier than thou hypocrites. Many oil technicians who
only work on oil are often Luddites and refuse to acknowledge superior technologies
.....I shall get off my high horse and get back to work..............